Hypercapnia: Difference between revisions

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== Introduction ==
== Introduction ==
Hypercapnia is when there is too much carbon dioxide (CO2) in the blood. This is normally caused by hypoventilation of the body which leads to CO2 retention. Hypercapnia is defined when the PaCO2 is greater than 4.2kPa on an [[Arterial Blood Gases|arterial blood gas]] (ABG).<ref name=":0">Patel S, Miao JH, Majmundar SH. [https://www.ncbi.nlm.nih.gov/books/NBK482456/#article-18844.r1 Physiology, Carbon Dioxide Retention.] InStatPearls [Internet] 2020 Feb 12. StatPearls Publishing.</ref>  
Hypercapnia is when there is too much carbon dioxide (CO2) in the blood. This is normally caused by hypoventilation of the body which leads to CO2 retention. Hypercapnia is defined as PaCO2 greater than 4.2kPa on an [[Arterial Blood Gases|arterial blood gas]] (ABG).<ref name=":0">Patel S, Miao JH, Majmundar SH. [https://www.ncbi.nlm.nih.gov/books/NBK482456/#article-18844.r1 Physiology, Carbon Dioxide Retention.] InStatPearls [Internet] 2020 Feb 12. StatPearls Publishing.</ref>  


Hypercapnia can eventually cause hypoxaemia due to reduced respiratory drive.   
Hypercapnia can eventually cause hypoxaemia due to reduced respiratory drive.   


However; hypercapnia can also be caused by long term [[hypoxaemia]] which causes the body to compensate leading to increased CO2 in the blood. This is known as type 2 [[Respiratory Failure|respiratory failure]].  
However; hypercapnia can conversely be caused by long term [[hypoxaemia]] which causes the body to compensate leading to increased CO2 in the blood. This is known as type 2 [[Respiratory Failure|respiratory failure]].  


== Type 2 respiratory failure ==
== Type 2 respiratory failure ==
Type 2 respiratory failure is defined as: PaCO2 is greater than 4.2kPa and PaO2 is less than 8kPa.<ref name=":0" /> (these ranges can differ slightly depending on the book or article).<ref>Kenyon K, Kenyon J. The Physiotherapist's Pocketbook. Essential Facts at your Fingertips. 2nd ed. London: Churchill Livingstone, Elsevier. 2009.</ref>
Type 2 respiratory failure is defined as: PaCO2 greater than 4.2kPa '''and''' PaO2 less than 8kPa.<ref name=":0" /> (these ranges can differ slightly depending on the book or article).<ref>Kenyon K, Kenyon J. The Physiotherapist's Pocketbook. Essential Facts at your Fingertips. 2nd ed. London: Churchill Livingstone, Elsevier. 2009.</ref>


is characterized by alveolar hypoventilation and increased carbon dioxide pressure(PaCO2). It is caused by loss of CNS drive, impaired neuromuscular competence, excessive dead space or increased mechanical load. Arterial carbon dioxide pressure PaCO2 is > 50mmHg. Commonly caused by myasthenia gravis, head injuries, polyneuropathies, muscular dystrophy, kyphoscoliosis, flail chest, obesity hypoventilation syndrome, advanced chronic bronchitis and emphysema.
It is caused reduced respiratory drive which commonly is due to a [[Neurological Disorders|neurological]] impairment. These neurological impairments could be traumatic or insidious in nature.
 
Type 2 respiratory failure is also common in advanced [[COPD (Chronic Obstructive Pulmonary Disease)|COPD]] patients due to: long term hypoxaemia or lack of gas exchange occurring in the alveoli thanks to poor tissue quality. <ref>McEvoy RD, Pierce RJ, Hillman D, Esterman A, Ellis EE, Catcheside PG, O’Donoghue FJ, Barnes DJ, Grunstein RR. [https://thorax.bmj.com/content/64/7/561.short Nocturnal non-invasive nasal ventilation in stable hypercapnic COPD: a randomised controlled trial.] Thorax. 2009 Jul 1;64(7):561-6.</ref>
 
On the contrary to hypoxaemia the patient will present as drowsy and with low respiratory rate as a result of the increased CO2 in the brain. <ref name=":0" />


== Clinical signs ==
== Clinical signs ==
* Change of behavior
In an acute setting a hypercapnic patient may present with some or all of the following symptoms:
* headache
 
* Coma
{| class="wikitable"
* Warm extremities
!Sign
* Astrexis
!Clinical feature
* Papilloedem
!Observation
|-
|Tachycardia
|Increased heart rate
|HR > 100 bpm
|-
|Dyspnoea
|Deranged respiratory rate
|RR inconsistent
|-
|Bradypnea
|Low respiratory rate
|RR < 12 bpm
|-
|Flushed skin
|Redness of face or body
|May be hyperthermic (not always)
|-
|Hot calor
|Warm extremities
|May be hyperthermic (not always)
|-
|Altered mental state
|Confusion, drowsy, difficult to wake
|
|-
|Astrexis
|Arm flapping
|Jerking motion of the hands, inability to stay still
|}


== Pathology ==
== Pathology ==

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Introduction[edit | edit source]

Hypercapnia is when there is too much carbon dioxide (CO2) in the blood. This is normally caused by hypoventilation of the body which leads to CO2 retention. Hypercapnia is defined as PaCO2 greater than 4.2kPa on an arterial blood gas (ABG).[1]

Hypercapnia can eventually cause hypoxaemia due to reduced respiratory drive.

However; hypercapnia can conversely be caused by long term hypoxaemia which causes the body to compensate leading to increased CO2 in the blood. This is known as type 2 respiratory failure.

Type 2 respiratory failure[edit | edit source]

Type 2 respiratory failure is defined as: PaCO2 greater than 4.2kPa and PaO2 less than 8kPa.[1] (these ranges can differ slightly depending on the book or article).[2]

It is caused reduced respiratory drive which commonly is due to a neurological impairment. These neurological impairments could be traumatic or insidious in nature.

Type 2 respiratory failure is also common in advanced COPD patients due to: long term hypoxaemia or lack of gas exchange occurring in the alveoli thanks to poor tissue quality. [3]

On the contrary to hypoxaemia the patient will present as drowsy and with low respiratory rate as a result of the increased CO2 in the brain. [1]

Clinical signs[edit | edit source]

In an acute setting a hypercapnic patient may present with some or all of the following symptoms:

Sign Clinical feature Observation
Tachycardia Increased heart rate HR > 100 bpm
Dyspnoea Deranged respiratory rate RR inconsistent
Bradypnea Low respiratory rate RR < 12 bpm
Flushed skin Redness of face or body May be hyperthermic (not always)
Hot calor Warm extremities May be hyperthermic (not always)
Altered mental state Confusion, drowsy, difficult to wake
Astrexis Arm flapping Jerking motion of the hands, inability to stay still

Pathology[edit | edit source]

[4]

Resources[edit | edit source]

  • bulleted list

References[edit | edit source]

  1. ↑ 1.0 1.1 1.2 Patel S, Miao JH, Majmundar SH. Physiology, Carbon Dioxide Retention. InStatPearls [Internet] 2020 Feb 12. StatPearls Publishing.
  2. ↑ Kenyon K, Kenyon J. The Physiotherapist's Pocketbook. Essential Facts at your Fingertips. 2nd ed. London: Churchill Livingstone, Elsevier. 2009.
  3. ↑ McEvoy RD, Pierce RJ, Hillman D, Esterman A, Ellis EE, Catcheside PG, O’Donoghue FJ, Barnes DJ, Grunstein RR. Nocturnal non-invasive nasal ventilation in stable hypercapnic COPD: a randomised controlled trial. Thorax. 2009 Jul 1;64(7):561-6.
  4. ↑ MrA91000. Pathology of Hypercapnia. Available from: https://www.youtube.com/watch?v=QrvhApnoKDM [last accessed 20/8/2012]
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